Fact 1: Afghans say they have a strong national identity.
That's a double statement:
1. intensity
2. <identification>
(And of course the answer depends on the framing of the question and the setting of that question.)
Fact 2: Afghans have had 30+ years of civil war.
Fun Fact, not all of them. Even funnier fact: Ethnic lines are a somewhat good divisor of who had civil war and who didn't.
Your theory on how to reconcile these two facts: Afghans are all blind, or liars, because in your opinion a country with a strong national identity should not have any infighting.
The mentioned theory is your theory on my theory, a theory I've never claimed, further more your assesment that led to you calling paradox is based on your wiew of afghanistan, not a common ground. So while i might scold I'd rather not.
Have I summed that up correctly?
Nope.
Here's my alternate theory: Having a strong national identity does not mean your country can't be deeply divided. Especially not when it's in the middle east, and two superpowers spend 15+ years arming everyone with hypermodern weapons and destroying every institution your country ever had.
1. Afghanistan is not in the middle east, it's not even in central asia to be true and it definitely isn't part of the indian subcontinent. Afghanistan is the roundabout for all of these places drawing upon them all and getting flak from them all.
2. There's been 4 superpowers involved (as well as some neighbours.), one of them twice. While they have been arming certain factions, inciting others they're also responsible for creating the institutions destroyed in the first place. The whole process has in it's current form been going on since Britain decided to expand and include a pashtuni principality on the now Pakistani side of the border and as far as the arming goes, Kiplings poem about the 10 rupee Jezzail stands today as it did back then.
Back to point, What did I actually say? When the States ability falters and falls apart as it has done in the past, the populace willingness to identify themselves as part of that crashed entity will be slim to nil, this is what happened in the post Soviet invasion climate where the state allegiance was blown away in favour of other entities, identity in that climate is not afghan but afghan suffix or just the suffix.